Do you ever wonder why trees begin to bud (发芽) earlier in some cities? Scientists finally found the answer but it's not very pleasant. New science suggests a relationship between light pollution and the timing when trees produce buds, which signals the arrival of the spring season.

    Light pollution is defined by the Lighting Research Center as the unwanted consequence of outdoor lighting such as street lights. Excessive (过多的) man-made light at night results in disturbed natural cycles, and also prevents the observation of stars and planets at night. But its effect on the environment goes beyond that.

    By studying some trees, researchers found out that trees that are more exposed to artificial lighting at night bud up to 7.5 days earlier than those at the natural nighttime setting. And they found out that light had a more significant effect than temperature when the buds came out. The early budding may cause problems for insects, which feed on leaves, and the birds which then feed on them in turn. Professor Richard Ffrench-Constant, who helped lead the research, explained that more than the budding of trees, the study implies the danger to the balance of the ecosystem. “At the moment, caterpillars (毛毛虫) are timed to hatch to make the most of the opportunities to feed on freshly budded leaves, and birds hatch in time to feed on the young caterpillar,” he said.

    Migratory (迁徙的) birds are also negatively affected by light pollution. The glare might confuse them and make them lose their flying sense. The phenomenon might explain why some birds accidentally knock into buildings.

    Such results stress the need to pursue studies that aim to measure the effect of light pollution. If the issue were left to continue, it is estimated that by 2100, spring would begin almost a full month earlier than it does today.

    If you're encouraged by the tiny house movement and think 160 square feet is just enough for your needs, you may want to contact the Academy of Construction and Design (ACAD) at IDEA Public Charter School in northeast Washington.

    Students in the program built a micro house with a kitchen, a bathroom, a sleeping loft with space for a queen-size bed and a storage loft, all set on a trailer for mobility. The exterior of the house was part of a continuous living exhibit in 2015 and was moved to the IDEA campus so students could work with builders to complete the interior earlier this year.

    McMahon said the D. C. government's approval to push companies to hire District residents was at odds with the school system not preparing students for careers in construction, exploring or electrical work. McMahon gathered industry and community leaders to establish ACAD in 2005, and he said 100 percent of the companies he contacted responded positively to the idea, including major firms such as JBG, Clark Construction, Hines Construction and Boston Properties.

    “When students make the connection between what they are learning a potential career, their academics improve dramatically,” said Carol Randolph, chief operating officer of the D. C. Students Construction Trades Foundation. “Some of them who didn't think college was an option now have a better chance because their classes have become relevant to a job.”

    “We teach them life skills and explain that even if you start as a laborer, there are opportunities to move up quickly,” he said. “We rewrite the story for them and explain that they can work for a few years, make good money, get promoted, and start their own business or go to school with less debts.”

    “Parents and school advisor can be the biggest obstacles because of the negative idea of construction as a blue-collar career,” Karriem said. “I get middle-school advisor on board to talk about the opportunities this education provides. These kids are learning lifelong skills that can help them in other fields, provide them with income and allow them to take care of their homes.”

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    The National Postal Museum is divided into galleries that explore America's postal history. Visitors will have a full picture of the creation and fantastic varieties of postage stamps.

    World of Stamps

    Video images bring stamps to life and attract visitors who explore the surrounding displays. Visitors encounter the world's first postage stamp — the 1840 Penny Black and learn how it revolutionized communication. Stamp images, including Dr. Martin Luther King's "I have a dream" speech and the stamp that helped raise almost $72 million dollars for breast cancer research, explain how stamps have shaped history and honored people and places worldwide.

Gems of American Philately

    Visitors have the opportunity of examining 13 of the most rare and highly valued stamps in the world of the stamp collection, including the most famous American stamp of all, the 1918 Inverted Jenny. A video explains why the Inverted Jenny and other stamps displayed here are the most valuable. The treasures in this area are rarely available for public viewing. Each tells a story about an important event in US history.

    Mail Marks History

    The markings on mail provide valuable clues to the surprising ways mail has been transported over time, including challenges and even disasters encountered along the way. You will understand these markings by following the journeys of three historic letters.

    Connect with US Stamps

    Visitors explore their own connections with stamps. At three touch screen tables, they create their own stamp collection based on the topics that interest them most. They can also create their own stamp designs. Visitors have the chance to view videos in which stamp designers talk about their craft, stamp collectors explain what they collect and why, and footage(片段) shows the process of making stamps.

New archaeological discovers suggest that trade between Europe and Asia along the Silk Road probably began in some form many centuries earlier than once thought. The findings, coupled with a widening range of scientific and historical research, could add a fascinating new page to the epic of the Silk Road.

The latest and most surprising discovery is pieces of silk found in the hair of an Egyptian mummy from about 1000 BC, long before regular traffic on the Silk Road and at least one thousand years before silk was previously thought to be used in Egypt. Other research may extend human activity along this route back even further, perhaps a million years to the migration of human ancestors into eastern Asia.

The official origin of East-West commerce along the road is usually placed in the late 2^nd century BC when an agent of the Chinese Emperor Wu-di returned from a dangerous secret mission across the western desert into the remote high country of Central Asia. The agent, Zhang Qian, travelled as far as Afghanistan and brought back knowledge of even more distant lands such as Persia, Syria and a place known as Lijien, perhaps Rome. Historians have called this one of the most important journeys in ancient times. His journey opened the way for what have been thought to be the first indirect contacts between the ancient world's two superpowers, China and Rome. Chinese silk, first traded to central Asian tribes for war horses and to the Parthians of old Persia in exchange for acrobats and ostrich eggs, was soon finding its way through a network of merchants to the luxury markets of Rome.

But the new discoveries show that Chinese silk was apparently present in the West long before the Han emperor started organized trade over the Silk Road. The research could change thinking about the early history of world trade and provide insights into the mystery of just how and when Europe and the Mediterranean lands first became aware of the glorious culture at the other end of Eurasia.

    One of the best-loved American writers was William Sydney Porter, or O. Henry. From 1893 he lived with his family in a house in Austin, Texas, which is now a museum. Visitors to Austin can see the house. It was saved from destruction (破坏) and turned into a museum in 1934. The museum is a good way to learn about the interesting life of the American writer.

    William Porter rented this house in Austin and lived there with his wife Athol and daughter Margaret for about two years. Many objects in the museum came from the Porters. Others did not. An important piece in the room is the original photo over here. It was taken there in the house about 1895. The piano there dates back to the 1860s. His wife took lessons on it when she first moved to Austin.

    Porter wasn't a successful writer in the beginning. He worked on a farm, in a land office and bank. He also loved words and writing. The museum has a special proof (证明) of Porter's love of language—his dictionary. It is said that he had read every word in that dictionary.

    Later William Porter was forced to leave Austin because he was charged (指控) with wrongdoing at the bank and lost his job. Because he was afraid of a trial (审判), he left the country secretly. But he returned because his wife was dying. After her death, he faced the trial and served three and a half years in a prison in Ohio.

    William Porter would keep his time in prison a secret. But there was one good thing about it. It provided him with time to write. By the time he was freed, he had published 14 stories and became well-known as O. Henry. Porter later moved to New York City and found great success there. He published over 180 stories in the last eight years of his life.

A short period of sleep taken during the day is known as a nap. Naps don't just have benefits for adults at work, though. They could also help pupils to make the most of their school day. Studies have shown that a 20 to 30-minute "beauty sleep" makes people more alert and focused. This improves people's ability to remember new information, which would help school children concentrate during lessons. Experts say that napping also improves brain functions, such as memory and the ability to complete difficult tasks.

The school day starts early, which means that pupils don't always get enough sleep because there's no chance to have a lie-in（睡懒觉. Adding naptime during the school day would help exhausted pupils to make up for any sleep they've lost from getting up so early.

There are long-term benefits to taking a short nap, too. According to a recent study from University College London, the brains of people who have regular naps are bigger than those who don't. People's brains naturally shrink (萎缩）when they grow old, and the results showed that little sleeps can help people's brains to age more slowly.

Although a nap can seem like a good idea, going to sleep for too long can actually make you feel worse. It's not very pleasant to wake up from a daytime nap feeling confused and sleepy. Napping during the day can also have a negative impact on how well you sleep at night. This can create a cycle of not being able to sleep well at night, leaving you feeling even more tired in the daytime. Sleep expert Dr Clete Kushida said, "It's generally recommended to maximize(最大化） sleep at night."

Another consideration is that there really isn't time in the school day for pupils to go to sleep. Some parents and teachers are concerned that it would cause children to miss too much lesson time. Pupils might take advantage of the system and use their need for a nap as an excuse to get out of lessons.

So, what do you think? Should school allow kids to have naps, or should you wait until the evening to catch up on your sleep?